1. Field of the Invention
The present invention relates in general to the ignition of fuels and relates in particular to the ignition of jet aircraft fuels at high altitudes using a plasma jet igniter.
2. Description of Prior Developments
Efforts have been underway for many years to improve the relight capability of jet engines and the like, particularly when such engines are operating at high altitudes and/or under adverse weather conditions. For example, jet aircraft operation within turbulent weather such as accompanies thunderstorms can cause a jet engine to "flame out".
It is critical that an ignition system be provided which will reliably relight the jet engine combustor during flight. Reliability of a relight system is particularly important at high altitudes where low entrance pressure and temperature conditions exist while the engine is "windmilling".
The ability to relight a jet engine at high altitudes is dependent upon the capability of the ignition system, the combustor geometry and air flow split, the quality of the spray produced by the fuel nozzle, the fuel properties and the combustor inlet conditions during windmilling. Of all of these factors, focus is presently concentrated on improvements in ignition system performance.
Conventional aircraft engine ignition systems include a spark igniter energized by a high voltage exciter circuit with a spark igniter located in the primary zone of the combustor. The spark discharge ignites a mixture of fuel and air in the combustor's primary zone and produces a kernel of hot combustion products. If the rate of heat loss from the ignition kernel is less than the rate of heat production in the kernel, the ignition front advances leading to combustor light-off. Most conventional ignition systems require a nearly stoichiometric fuel-air mixture in the vicinity of the igniter and favorable aerodynamic conditions such as a large recirculation zone for optimal operation.
A need currently exists for an improved ignition system for a jet engine combustor which reliably operates under wider operating conditions than possible using conventional spark igniters. A particular need exists for such a system which will reliably operate at high altitudes and/or under adverse operating conditions such as exist during turbulent weather. A further need exists for such a system which does not require a stoichiometric fuel-air mixture for light-off.